(a) Field of the Invention
The present invention relates to a vehicle traveling position detecting system. More particularly, the present invention relates to a vehicle traveling position detecting system, which is used in a lane marker system for guiding a vehicle along a desired pathway.
(b) Description of the Prior Art
In a lane marker system, a plurality of magnetic markers are arranged along a pathway of vehicles and a magnetic sensor array including a plurality of magnetic sensors are mounted aboard a traveling vehicle to guide the vehicle along the pathway while detecting the magnetic field distribution generated from the magnetic markers. The magnetic field distribution generated from the magnetic markers is detected for accurately assessing the vehicle position with respect to the pathway.
In the lane marker system, when the magnetic field distribution is detected by the magnetic sensors while the vehicle is traveling, many undesirable elements on the road may disturb the magnetic field. The magnetic disturbances raise problems such as erroneous detection, detection failure and detection accuracy deterioration in the lane marker system. To solve the above-mentioned problems various measures are proposed.
FIG. 1 is a block diagram of a vehicle traveling position detecting sensor described in Japanese Patent Laid-Open Publication No. Hei. 11-72304. As shown in FIG. 1, in the vehicle traveling position detecting system, five magnetic sensors 81 to 85 detect the magnetic field generated from magnetic markers that are arranged along a pathway of a traveling vehicle, whereby each sensor generates a detected magnetic field signal in accordance with the magnetic field thus detected. An input circuit unit 86 receives the detected magnetic field signals from the sensors 81 to 85 at different times and performs analog-to-digital (A/D) conversion of the detected magnetic field signals. After that, the input circuit unit 86 transmits the detected data, which is obtained by converting the analog signals into digital data, consecutively to a peak detection unit 89, a sensor selection unit 90, a differential calculation unit 88 and a lateral displacement calculation unit 92.
The differential calculation unit 88 differentiates the detected data and a comparison/judgement unit 95 compares the differentiated value (differential) of the detected data against a predetermined threshold value to determine whether the differentiated value is xe2x80x9clargerxe2x80x9d or xe2x80x9csmallerxe2x80x9d than the threshold value.
When the judgement result by the comparison/judgement unit 95 is xe2x80x9clargerxe2x80x9d, a control unit 87 performs a control operation so that the input circuit unit 86 receives new detected signals from the sensors 81 to 85. When the judgement result is xe2x80x9csmallerxe2x80x9d, the control unit 87 controls the lateral displacement calculation unit 92 based on signals from the peak detection unit 89 and the sensor selection unit 90. The lateral displacement calculation unit 92 temporarily stores the detected data and calculates the lateral displacement with respect to the magnetic markers. A sensor position correction unit 93 calculates the correction value with respect to the sensor position based on the lateral displacement, and an output unit 94 converts the correction value into an analog value using a D/A converter to output the analog correction value.
The conventional vehicle traveling position detecting system as described above is capable of obviating erroneously detected data, ascribable to a noise component included in the detected signals from the sensors 81 to 85 by using the processes including: comparing the differentiated value against the threshold value; judging that the detected signals are the signal components derived from the magnetic field distribution generated from the magnetic marker when the differentiated value is smaller than the threshold value; judging that the detected signals are the noise components when the differentiated value is larger than the threshold value; and separating the signal components from the noise components based on the results of the judgement.
The noise component described in the above publication using the conventional technology corresponds to a pulse noise component that disturbs the magnetic field distribution generated from the magnetic markers in a short fluctuation period. However, another pulse noise component, other than the above-described pulse noise component, also exists that disturbs the magnetic field distribution generated from the magnetic markers in a long fluctuating period. The conventional vehicle traveling position detecting system is not capable of detecting or removing the latter noise component.
It is therefore an object of the present invention to solve the above problem in the conventional technique and to provide a vehicle traveling position detecting system which is capable of detecting a lateral displacement with a high degree of accuracy while the vehicle is traveling on the road.
The present invention provides, in a first aspect thereof, a vehicle travelling position detecting system including a magnetic sensor mounted on a vehicle for detecting a magnetic field generated by one of magnetic markers arranged in a travelling direction of the vehicle to output a detected magnetic field signal, a speed sensor for detecting a travelling speed of the vehicle, a delay unit for delaying the detected magnetic field signal by a delay time calculated based on the detected travelling speed to output a delayed magnetic field signal, a subtracter for calculating a difference between the detected magnetic field signal and the delayed magnetic field signal to output a difference signal, a displacement calculating unit for calculating based on the difference signal a displacement of the vehicle with respect to the one of the magnetic markers in a lateral direction normal to the travelling direction.
The present invention also provides, in a second aspect thereof, a vehicle travelling position detecting system including a magnetic sensor mounted on a vehicle for detecting a magnetic field generated by one of magnetic markers arranged in a travelling direction of the vehicle to output a detected magnetic field signal, a speed sensor for detecting a travelling speed of the vehicle, a sample/hold circuit for sampling the detected magnetic field signal at a specified sampling period to output a series of sampled magnetic field signals, a first memory section for storing the series of sampled magnetic field signals, a subtracter for calculating a difference between each two of the series of sampled magnetic field signals sampled at a specified interval to output a series of difference signals, a second memory section for storing the series of difference signals, and a displacement calculating unit for calculating based on the series of difference signals a displacement of the vehicle with respect to the magnetic markers in a lateral direction normal to the travelling direction.
In accordance with the vehicle travelling position detection system of the present invention, noise existing in the magnetic filed from the magnetic marker and having a long term fluctuation period can be removed by the subtracter, whereby the difference signal has a higher accuracy of the detected magnetic field signal.
The above and other objects, features and advantages of the present invention will be more apparent from the following description, referring to the accompanying drawings.